var gulp = require('gulp');
var postcss = require('gulp-postcss');
var myplugin = require('postcss-plugin-px2units');
gulp.task('css', function () {
  var processors = [
    myplugin({
      viewportWidth: 3840, 
      viewportHeight: 2304
    })
  ];
  return gulp.src('./src/*.css')
    .pipe(postcss(processors))
    .pipe(gulp.dest('./dest'));
});